The present invention relates to an idling speed control system for an internal combustion engine featuring an electronic fuel injection system, preferably, but not exclusively, of the single injection type. The said system provides for controlling idling speed both during and subsequent to warming up the engine, that is, whenever minimum engine speed falls, for example, due to connection of additional loads such as the air conditioner, or as a result of varying external parameters, such as gradients.
Idling of an internal combustion engine, mainly when starting and warming up the engine, is conveniently controlled by a heat-sensitive element which, when subjected to the gradually increasing temperature of the engine cooling water, gradually pushes out a piston and, via a number of lever systems, gradually reduces the minimum aperture of a throttle valve controlling air supply to the engine. A major drawback of control systems of the aforementioned type is that response time for reducing the minimum aperture of the said main throttle valve is relatively slow, with the result that the engine is maintained at a higher than theoretically optimum idling speed. The poor precision and relatively slow response of known control systems of the aforementioned type are particularly disadvantageous when applied to electronic injection systems, which, on the contrary, are programmed for ensuring greater control efficiency of the engine under all operating conditions. Idling speed control systems have been proposed for overcoming the aforementioned drawbacks, but these are invariably highly sophisticated and, therefore, expensive.